When Life Gives You Lemons, Assess Their Mating Characteristics, Growth, and Survival

Alex Aines, Shark Researcher and TOF Intern

At the beginning of April I arrived at Bimini Biological Field Station in the Bahamas for a 3-month stay. I am currently working at the station’s Shark Lab and assisting in various research projects with an amazing team of 20-30 year old individuals from all over the world, including Brazil, England, US, Canada, Australia, and France.

As soon as I exited the airport I was whisked right onto a boat to tag hammerheads, and since then it’s been a whirlwind of coming into contact with seven different species of sharks, learning the ins and outs of the lab and being part of an amazing, international crew. Since I arrived, one thing has stayed constant: the perpetual preparation for the biggest research project of the year, PIT.

May 24th was a day we heard about for months: we built countless holding pens, inventoried pen mesh, scavenged cinder blocks, checked all of our equipment, repaired gillnets and boats and readied ourselves for a total of 12 days in the field where we would tag and collect data on juvenile lemon sharks in North Bimini.  image (4).jpg

We call this annual project, PIT, which stands for Passive Integrated Transponder, the type of tags we implant in these juvenile lemon sharks. This type of tag is comparable to the size of a grain of rice, and when scanned provides a unique “barcode” for each individual. We then use this string of numbers to identify each individual shark. This is the same type of tag that people often implant in their pets. It has a low shed rate and zero harmful impact on the shark. We inject these tiny tags into the area around the base of the dorsal fin and it is there they remain for life. 

So what is the purpose of PIT? What kind of data do we collect? The 12 days we spend in the field are split between two separate locations, Sharkland and the North Sound. These two areas are nurseries for juvenile lemon sharks. Bimini is unique in that it has some of the only viable nursery grounds for many miles. Because of this, these baby sharks cannot migrate out of this area for at least 3 years for fear of being preyed upon. The lemons usually stay in the mangroves for 4-5 years and do very well in semi-captivity. We use gillnets (normally illegal in Bimini, but we have a research permit) to capture the sharks; there are 3 different nets set up in each area, and we do checks on these nets every 15 minutes. If we capture a shark, we quickly transport it to a nearby pen, where the tagging team works it up. This team weighs, measures, sexes, takes a DNA and isotope sample and tags the shark. The sharks are then moved into holding pens based on their precaudal length. Some of the sharks are then selected to be part of behavioral trials run by the PhD students at Bimini. 

Post-capture holding penThis is our 21st year of PIT, and in those 21 years we have collected around 4,000 genetic samples. We are specifically looking at survival, mating characteristics and growth. On average, we catch about 200 sharks each year between both nurseries. The first two days are usually the most hectic (our first day brought in 64 little lemons) and then numbers tend to decrease. In our first 6 days, we caught a total of 107 sharks! We catch about 99% of the juvenile lemon sharks in these nurseries.

If one of us briefly described the surreal PIT experience, you would likely think we are out of our minds. Typically, we set out our nets around 6pm and we haul around 6am. We spend 12 glorious hours on the water combatting rain, bugs and boats that spontaneously decide to not function properly. We live for the midnight food runs (the joys of being on a nocturnal schedule) where we get dinner, snacks and hot beverages. And even with all of these factors, our group does a fantastic job of making what could be a relatively uncomfortable situation incredibly fun. 

There are 3-4 people per boat, and this is your team. Your team remains the same for 3 days and then we change everything up. We rotate jobs, including driving the boat, lighting up the net and doing walk checks if necessary. We have recently finished up a week-long hiatus between nurseries, which we used to fix everything, do behavioral trials and release sharks! We are now on our final leg of PIT, with about 200 sharks captured and still 3 days to go.

So far it has been a pleasure to be part of such an enthusiastic team and one so passionate about shark research and conservation. We are all extremely lucky to be a part of such important work, and if you want to learn more about the lab and its research, visit:  http://www.biminisharklab.com/